The present invention relates a method of manufacturing a semiconductor device, and particularly to a technology which is effective when applied to the manufacturing of a semiconductor device including an exposure step using a reticle.
In a manufacturing step of a semiconductor device, when a film over a semiconductor substrate is patterned using photolithographic technique, exposure to light for projecting a pattern over a reticle (photomask) is performed to form a photoresist film into a desired shape. At this time, a part of exposure light is blocked by passing through the reticle, and the exposure light transmitted by the reticle is reduced in size by passing through a projection lens to irradiate a surface of a semiconductor substrate (wafer). In this manner, the pattern provided over the reticle is reduced in size and projected on the photoresist film. At this time, to cause the light transmitted and projected by the projection lens to be focused on the main surface of the semiconductor substrate, a known method is used in which an automatic focus correction mark (alignment mark) provided over a recto (region where products are not formed) located outside an actual device region in a center portion of the reticle is projected on a photosensitive substrate (detector) formed over a wafer stage over which a semiconductor substrate is mounted to determine an optimum focus position.
In Japanese Unexamined Patent Publication No. 2005-129781 (Patent Document 1), it is stated that alignment marks are provided over a chip region and thereby increase the occupation ratio of the chip region over a wafer to a value higher than in a case where alignment marks are provided in a scribe line region. Here, it is stated that respective alignment marks are disposed in at least two chips through which an X-axis and a Y-axis passing through the center of a reticle extend.
In Japanese Unexamined Patent Publication No. Hei 5(1993)-182897 (Patent Document 2), an exposure apparatus is described which uses a value measured using a TTL (Through the Lens) autofocus system to perform exposure in an optimal focal plane in consideration of the properties of a projection lens.
In Japanese Unexamined Patent Publication No. Hei 4(1992)-58250 (Patent Document 3), it is stated that, by using a slit-like correction pattern formed over a reticle, an amount of displacement between an autofocus system and an exposure optical system is automatically corrected.
In Japanese Unexamined Patent Publication No. Hei 9(1997)-260269 (Patent Document 4), it is stated that, in a projection exposure apparatus, a pattern formed over a reticle is projected onto a photosensitive substrate by exposure, the state of an image of the pattern formed on the photosensitive substrate is detected to allow an optimal focus position to be determined, and the optimal focus position over a stage is corrected based on a plurality of mark focus positions. Here, marks (light transmitting portions) for correcting the focus position are provided outside the actual device region of the reticle.